Where Is Internal Redirect Example?

Hi. I'm using litespeed for some months and feel that the server is great. Howerver now I need it to be able to transfer large data (1 GB+) for download by user, but I don't know how.

Using php readfile is useless, always cut off in the middle of download. I've read about the litespeed's Internal Redirect but don't know how to put it into action. I've searched the forum & googled all day long, and can't find it either.